In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, transmission schemes and reception schemes based on the use of narrow beams might be needed at high frequencies to compensate for propagation losses. For a given communication link, a beam can be applied at both the network side (such as at the transmission and reception point (TRP) of a network node) and the user side (such as at wireless devices served by the network node). A beam pair link (BPL) is defined by the beam used by the TRP (denoted TRP beam) for communicating with the wireless device and the beam used by the wireless device (denoted WD beam) for communicating with the TRY. Each of the TRP beam and the WD beam could be used for any of transmission and reception. Likewise, there could be separate BPLs for downlink communications (Where the TRP beam is a transmission (TX) beam and where the WD beam is a reception (RX) beam) and uplink communications (where the TRP beam is an RX beam and where the WD beam is a TX beam).
In general terms, a beam management procedure is used to discover and maintain BPLs. A BPL is expected to be discovered and monitored by the network using measurements on downlink reference signals used for beam management, such as channel state information reference signals (CSI-RS). The CSI-RS for beam management can be transmitted periodically, semi-persistently or aperiodic (such as being event triggered) and they can be either shared between multiple wireless devices or be device-specific. In order to find a suitable TRP beam the TRP transmits CSI-RS in different TRP TX beams on which the wireless devices performs reference signal received power (RSRP) measurements and reports back the N best TRP TX beams (where the value of N can be configured by the network). Furthermore, the CSI-RS transmission on a given TRP TX beam can be repeated to allow the wireless device to evaluate suitable WD beams, thus enabling so-called WD RX beam training.
The wireless devices and/or the transmission and reception point (TRP) of the network node could implement beamforming by means of analog beamforming, digital beamforming, or hybrid beamforming. Each implementation has its advantages and disadvantages. A digital beamforming implementation is the most flexible implementation of the three but also the costliest due to the large number of required radio chains and baseband chains. An analog beamforming implementation is the least flexible but cheaper to manufacture due to a reduced number of radio chains and baseband chains compared to the digital beamforming implementation. A hybrid beamforming implementation is a compromise between the analog and the digital beamforming implementations. As the skilled person understands, depending on cost and performance requirements of different wireless devices, different implementations will be needed.
One drawback with an analog beamforming implementation is that the TRP only can transmit or receive in one beam at a time (assuming one antenna array being active at the time, and the same beam being used for both polarizations, which usually is the case in order to counteract dropped signal strength due to polarization mismatching).
For served wireless devices with high mobility, beam management may require significant amount of overhead signalling due to the fact that the serving beam has to be updated frequently, thus resulting in a high number of handovers between different beams at one and the same TRP. This overhead is extra severe when the TRP is using analog beamforming, due to the fact that only one TRP beam then can be used at each time instance, which for example makes TRP beam sweeping (needed to find the new TRP beam) costlier.
Hence, there is still a need for improved beam management.